[gjs: 1/2] gi: fix the usage of closure in CallbackIn::release

[Philip Chimento <pchimento src gnome org>]

commit 8e1c28156b32765b4f6b2e41007281ddb07ccdee
Author: Xi Ruoyao <xry111 mengyan1223 wang>
Date:   Mon Mar 28 20:18:12 2022 +0800

    gi: fix the usage of closure in CallbackIn::release
    
    We were getting closure pointer from in_arg.  Unfortunately, in_arg
    contains the native closure pointer, which does not equals to of the
    pointer to ffi_closure if libffi is built without
    `--disable-exec-static-tramp`.
    
    I guess gjs has never been really tested with such a libffi build :).

 gi/arg-cache.cpp | 6 +++++-
 gi/function.h    | 4 ++++
 2 files changed, 9 insertions(+), 1 deletion(-)
---
diff --git a/gi/arg-cache.cpp b/gi/arg-cache.cpp
index 177f246f4..ef9671aea 100644
--- a/gi/arg-cache.cpp
+++ b/gi/arg-cache.cpp
@@ -708,6 +708,8 @@ struct CallbackIn : SkipAll, Callback {
 
     bool release(JSContext*, GjsFunctionCallState*, GIArgument*,
                  GIArgument*) override;
+ private:
+    ffi_closure *m_ffi_closure;
 };
 
 using CArrayIn = ExplicitArrayIn;
@@ -831,6 +833,7 @@ bool CallbackIn::in(JSContext* cx, GjsFunctionCallState* state, GIArgument* arg,
     if (value.isNull() && m_nullable) {
         closure = nullptr;
         trampoline = nullptr;
+        m_ffi_closure = nullptr;
     } else {
         if (JS_TypeOfValue(cx, value) != JSTYPE_FUNCTION) {
             gjs_throw(cx, "Expected function for callback argument %s, got %s",
@@ -855,6 +858,7 @@ bool CallbackIn::in(JSContext* cx, GjsFunctionCallState* state, GIArgument* arg,
                 return false;
         }
         closure = trampoline->closure();
+        m_ffi_closure = trampoline->get_ffi_closure();
     }
 
     if (has_callback_destroy()) {
@@ -1411,7 +1415,7 @@ bool CallerAllocatesOut::release(JSContext*, GjsFunctionCallState*,
 GJS_JSAPI_RETURN_CONVENTION
 bool CallbackIn::release(JSContext*, GjsFunctionCallState*, GIArgument* in_arg,
                          GIArgument* out_arg [[maybe_unused]]) {
-    auto* closure = gjs_arg_get<ffi_closure*>(in_arg);
+    ffi_closure *closure = m_ffi_closure;
     if (!closure)
         return true;
 
diff --git a/gi/function.h b/gi/function.h
index 799c14903..b70c7e297 100644
--- a/gi/function.h
+++ b/gi/function.h
@@ -57,6 +57,10 @@ struct GjsCallbackTrampoline : public Gjs::Closure {
 #endif
     }
 
+    ffi_closure* get_ffi_closure() const {
+        return m_closure;
+    }
+
     void mark_forever();
 
     static void prepare_shutdown();